The invention is directed to a shock absorbing wheel suspension apparatus and related method. Although the preferred embodiment is described with respect to the rear suspension on a mountain bike, persons of ordinary skill in the art will understand that the invention may be readily utilized in other configurations and devices, especially those using chain drive power on a suspended wheel, including (by way of example and not by way of limitation) suspensions for motorcycles, tricycles, four-wheeled vehicles, and other vehicles.
The following table sets forth U.S. patents which may be material to the patentability of the invention:
Also, a number of Internet websites currently display bicycles having wheel suspensions. Examples can be seen at the websites for the following companies: Cyber Cyclery, Intense Cycles, Inc., GT Bicycles, Mountain Cycle, Schwinn, and Ventana Mountain Bikes.
Although current bicycle suspension designs typically include shock absorption capabilities that are intended, among other things, to provide comfort and safety and, ideally, to allow the tires to maintain contact with the ground (even on uneven surfaces) and have traction on rough, steep climbs and descents, current designs have a number of inherit faults or shortcomings.
Among other things, suspensions typically permit riders to descend with greater speed, control and comfort. Moreover, although the suspension provides some benefits for climbing (and, as indicated, definitely provides important benefits to descending), many (if not most) current designs are actually generally considered a hindrance to climbing. During climbing, most prior art suspensions xe2x80x9csuckxe2x80x9d power (as described below); the less kinetically efficient designs typically xe2x80x9csuckxe2x80x9d the most power during climbing. In addition, many prior art suspension designs are so bulky or contorted that they add undesirable weight to the bicycle, which also xe2x80x9csucksxe2x80x9d power from the rider, especially during climbing.
While some of the benefits provided by the invention might be achievable by using idler pulleys and other components, such approaches presumably would add weight (for the extra components) and the additional drag of pulleys would of course require additional energy to propel (from the rider, the engine, etc.)
In addition, it would presumably be difficult (or even impossible) to utilize such a pulley system on a bicycle with otherwise conventional industry standard components (gears, derailleurs, etc.). In other words, such pulley approaches might not be able to use an xe2x80x9coff-the-shelfxe2x80x9d set of gears.
Several examples of these shortcomings are further discussed below.
1. Pedaling power Loss Due to Drive Torque Induced Suspension Movement (xe2x80x9cTorque Reactivexe2x80x9d Suspensions).
All current bicycle rear suspensions of which the inventors are aware have a tendency to either compress or extend the rear suspension when subjected to drive chain and wheel drive loads. Designs that compress the rear suspension cause the rider""s power to be used for compressing the shock absorber. The potential energy transferred to the shock absorber is dissipated as heat by the damping medium in the shock absorber. Designs that extend the suspension under load waste power by lifting the mass of the bike and rider with each stroke. Designs that attempt to exploit the chain loads to create torque against the suspension create a binding action of the suspension under pedal torque loads, which reduces ride quality and limits compliance-induced traction under hard pedaling.
Because an average human being can generate a maximum of about three quarters (xc2xe) horsepower and can do so for only a very short time, and can generate only about {fraction (1/10)} of a horsepower for extended periods, even small power losses can have a significant effect on the rider and the riding experience. In the designs described in the preceding paragraph, potential energy is typically returned out of phase to the pedals"" and cranks"" power stroke and is thus wasted as heat dissipated in the damper instead of power used to propel the bicycle forward.
In addition, suspension designs that are torque reactive feel mushy, sluggish and unresponsive to pedaling input.
Also, with a typical rear suspension design, the wheel follows an arc-like path when encountering a bump, forcing the wheel to be displaced in a forward as well as an upward direction (in contrast, and as shown by a comparison of FIGS. 3 and 6 of the preferred embodiment of the invention, as discussed below, the present invention provides much more nearly vertical wheel motion in response to bumps). Thus, when absorbing shocks, the prior art wheels must travel forward, frequently in an uphill direction. This increases the bump shock force transmitted to the sprung portion of the bicycle because the wheel is not moving perpendicularly away from the bump. It also requires more forward drive energy from the rider to overcome the resulting xe2x80x9crearwardxe2x80x9d component of such bump forces. Additionally, the suspensions will kickback that motion to the pedals, causing additional wasted energy and muscle irritation and premature fatigue from the uneven loading while pedaling.
This and other of the problems discussed herein are especially acute in human-powered devices such as bicycles, because the human power plant typically provides such low RPM that the jacking or torque reaction happens (and is felt) with each revolution, rather then just xe2x80x9concexe2x80x9d as might be experienced under acceleration from an internal combustion engine, for example.
2. Lock Up of the Rear Suspension Caused by Brake Induced Torque.
Almost all current art bicycle rear suspension designs place the anchor for their rear brakes (be it either a disc brake caliper or traditional rim surface caliper type brakes) in a position where the application of brake force causes an extending force or xe2x80x9cjackingxe2x80x9d to be exerted on the rear suspension. This xe2x80x9cjackingxe2x80x9d force causes the rear suspension to lose its effectiveness under heavy braking loads, as the jacking may lock out the suspension, and/or cause the rear of the bike to raise, forcing the rider forward and shifting the center of mass over the front wheel, thereby causing instability of the bike and rider. This jacking can manifest itself as xe2x80x9cwheel hopxe2x80x9d and instability under heavy braking on rough surfaces.
Current suspension designs (as opposed to rigid rear linkages) create this unsafe (or at least difficult-to-control) jacking. Some designs utilizing a disc brake will counter these jacking forces by anchoring the brake forces with a separate member attached to the frame away from the wheel suspension. Although this approach works to eliminate the brake xe2x80x9cjackingxe2x80x9d problem, it introduces additional weight and components (thus not lending itself to simple design), and may limit the bicycle frame""s kinetic responsiveness (which is one of the main points of having a suspension in the first place). Other brake arrangements actually stiffen or even lock out the suspension while braking, even though arguably the most important time for suspension functions are likely demanded while braking for obstacles or rough and technical terrain.
3. Proper Shock Absorber Motion Ratio.
The motion ratio of the bike""s shock absorber is critical to proper suspension operation. The motion ratio of the suspension bikes currently on the market runs the range from rapidly rising to rapidly falling. There are major drawbacks as you move toward either end of the spectrum.
A very rapid rising rate causes the suspension to be too soft and active in the initial part of the wheel travel, causing bobbing and wasting pedaling energy while quickly blowing through the initial travel on big bumps and xe2x80x9cG-outsxe2x80x9d (high load, long duration bump impulses), while eventually becoming non-compliant and harsh at later portions of the shock absorption motion. A rapid rising rate is caused by small xe2x80x9cbell crankxe2x80x9d shock rockers (or xe2x80x9crocker armsxe2x80x9d or xe2x80x9crocker linksxe2x80x9d or xe2x80x9cupper swingarmsxe2x80x9d) where the motion ratio is vastly changed through the suspension stroke due to the great change in angle created by the small rockers. Among other things, air shocks do not work well with rising rate suspensions as an air spring also has a rising rate which results in a very rapid rising rate.
A falling rate is the worst case scenario for a mountain bike""s suspension. A falling rate suspension is initially stiff and gets softer as the suspension travel goes through its stroke. A falling rate suspension is stiff and non-compliant on high frequency xe2x80x9cstutterxe2x80x9d bumps, while still blowing through the travel, bottoming out with great force on big bumps.
A suspension with a slight falling rate can work fairly well when combined with an air shock. Due to an air spring""s progressive nature, the resulting combination is a nearly linear wheel xe2x80x9cmotionxe2x80x9d rate. However, when a stiff spring is selected on a falling rate bike to prevent excessive bottoming, the suspension is very stiff and almost non-existent on small or ripple (or xe2x80x9cstutterxe2x80x9d) bumps.
In contrast, and as discussed herein, the preferred embodiment of the current invention provides a frame having an almost linear (described herein as xe2x80x9cprogressively linearxe2x80x9d) motion ratio. Persons of ordinary skill in the art will understand that perfect linearity would occur if the first 1 inch xe2x80x9ccompressionxe2x80x9d movement of the bicycle wheel resulted in xc2xc inch of compression of the shock member and every further 1 inch increment of bicycle wheel xe2x80x9ccompressionxe2x80x9d movement likewise corresponded to xc2xc inch of shock member compression. A graph of representative prior art motion ratios, as well as the motion ratios for the instant invention, is set forth in FIG. 3C. Because the preferred xe2x80x9cframexe2x80x9d of the suspension behaves linearly, a user can xe2x80x9cmakexe2x80x9d that same frame function either with a generally linear or progressive motion ratio, via the selection or adjustment of the shock absorbing member (which members come in a wide range of motion ratios and characteristics). As further described below, the preferred invention includes using longer rocker arms than any prior art of which the inventors are aware. The xe2x80x9crocker armxe2x80x9d is in fact so long that it is very nearly appropriate to call it an xe2x80x9cupperxe2x80x9d swingarm (in distinction from the xe2x80x9clowerxe2x80x9d swingarm element present in both the instant invention and (in broad concept) in many prior art designs. As indicated above, those prior art designs typically use a lower swingarm with the upper linkage formed by a xe2x80x9cbell crankxe2x80x9d or xe2x80x9crocker armxe2x80x9d.
This long xe2x80x9cupper rocker armxe2x80x9d in the preferred embodiment of the invention (along with the configuration and relative dimensions of the nose of that rocker arm) helps accomplish the desired alignment of the pivots in the linkage of the instant invention. This alignment accomplishes the linkage""s desired tracking of the xe2x80x9cinstant centerxe2x80x9d (xe2x80x9cICxe2x80x9d) so that it remains on or very near the chain tension line of the drive chain (thereby reducing or eliminating undesirable chain torque). In the preferred embodiment, as described herein, the linkage""s tracking keeps the IC on (during normal operating xe2x80x9cladenxe2x80x9d [meaning having the rider aboard the bicycle] mode of suspension) or very near (during any other point of suspension travel) that chain torque line. No other bicycle suspension (even other xe2x80x9cfour bar linkagesxe2x80x9d) of which the inventors are aware provides this beneficial tracking and/or the initially laden orientation.
4. Mechanically Simple, Elegant Design.
To address the various factors that determine performance of wheel suspension, bicycle rear suspensions have evolved into a wide range of complicated, typically unreliable, xe2x80x9cRube Goldbergxe2x80x9d-like devices.
In addition, it is generally more economic if a design can utilize xe2x80x9cstandardxe2x80x9d or xe2x80x9coff-the-shelfxe2x80x9d components, such as drive train and brake components, rather than requiring those components to be custom designed and manufactured.
Existing devices typically suffer from one or more of the foregoing exemplary shortcomings, in various degrees and combinations. Examples of some of the most common rear suspension designs are described below.
1. Horst-Link McPherson Strut.
Pioneered by AMP research, and used by Lightspeed, Rocky Mountain, Intense, Turner, Specialized and others.
The basic operating principle of these devices is illustrated in U.S. Pat. No. 5,509,679 to Leitner. As shown there, the lower pivoting arm or chainstay""s pivot axis is located at or below the horizon point of the tensioning run of the drive chain of the smallest chainring, and a rear swingarm pivot or lower link is located in front of the vertical axis of the rear axle and below the horizontal axis of the rear axles. This location provides a binding action, mentioned above, that resists chain-induced xe2x80x9cjackingxe2x80x9d up and down movement of the suspension. Among other things, the resistance to the chain-induced xe2x80x9cjackingxe2x80x9d is established by creating additional torques to counteract other torques and thus results in the aforementioned xe2x80x9cbindingxe2x80x9d.
Although this design is simple and lightweight, it has several negative performance indicators. While variations in designs utilizing a xe2x80x9cHorst-Linkxe2x80x9d can incorporate to varying degrees some of the following desirable characteristics: somewhat non-pedaling force torque reactive, somewhat non-brake torque reactive, all xe2x80x9cHorst Linkxe2x80x9d designs also exhibit to varying degrees the following undesirable characteristics (which one can generalize to have become accepted as the xe2x80x9cstate-of-the-artxe2x80x9d in bicycle full-suspension designs): somewhat responsive to pedal kickback from bump loads under pedaling force, reduced suspension activity due to mild to severe binding action of the suspension geometry, and most Horst-Link, McPherson strut bicycle rear suspensions suffer from a falling rate shock absorber motion ratio which varies greatly with frame size. The rear part of the bicycle frames are very flexible, due to the fact that the shock absorber shaft is a major structural member of the linkage. Not only is the shock shaft a very poor structural member (in part, typically, because of its small diameter), but the additional xe2x80x9clinkagexe2x80x9d loading on the shock also causes the shock unit to heat up and sometimes bind, resulting in premature wear and failure. Also, the suspension action is somewhat affected by pedal torque input. Mild binding action of the suspension under pedal torque loads reduces ride quality and limits compliance-induced traction under hard pedaling. This is a significant disadvantage on steep rough climbs. Brake torque and cornering loads cause shock bind. Brake load causes the suspension to jack upwards slightly. This design typically reacts to some degree to both brake- and pedal-induced torque loads, which loads vary dramatically with frame size and gear selection.
In contrast, and as more fully explained herein, the preferred embodiment of the invention prevents all these unwanted characteristics, specifically by utilizing the xe2x80x9cupper swingarmxe2x80x9d or rocker arm to help: (1) control the motion ratio of the frame, allowing for a selectable linear or progressive shock motion ratio (accomplishable, among other ways, by selecting from a wide variety of off-the-shelf shock units); (2) reduce or eliminate wheel twist and similar forces, such as by using a shockstay clevis (see FIGS. 2D-2I, for example) which holds the rear of the rockers firmly against lateral flex, along with the preferred rocker lateral brace at the midpoint and the preferred 8-mm bolts at the four linkage pivots (calculations indicate that this upper-swingarm/clevis/brace/bolts arrangement to be over 20% stiffer then the tubing used in most McPherson Strut designs; (3) have the linkage members"" instant center track the chain torque of the bicycle throughout the suspension motion (thereby eliminating, by way of cancellation, rather then binding, or reducing chain torque energy waste, as discussed herein).
2. High Single Pivot.
Used by Foes, Mountain cycle, Bolder, Pro Flex, Cannondale, Marin, and others.
The basic operating principle of these devices is illustrated in U.S. Pat. No. 5,217,241 to Girvin. The main pivot of the suspension is located at a point slightly above the chainline of the large chainwheel. This provides a lifting moment to the suspension which is slight in the large chainring and greater in the smaller chainrings. The lifting moment counteracts pedal and rider body movement-induced squat.
Although these designs can be somewhat simple in construction and somewhat non-pedal-torque reactive in a certain chainring-gear combinations, usually they are very pedal-torque reactive in the chainring farthest away horizontally from the pivot. In the small chainrings, these constructions typically lift the bike and rider with an energy-wasting xe2x80x9cinchwormxe2x80x9d bobbing effect with each pedal stroke and its accompanying chain torque. These suspensions do not respond to bump loads under hard pedaling, as bump force must overcome the lifting moment in order to move the wheels in reaction to a bump. Also, due to their arc-like wheel path during shock absorption motion, the wheelbase dimension changes throughout the wheel""s stroke, causing kickback while pedaling. These designs are usually very brake-torque reactive, which causes the suspension to extend and lock out. These typically require a bulky and sometimes heavy swingarm, as well as a huge overbuilt pivot and pivot supports, to maintain sufficient or desirable rigidity.
This prior art suspension is inexpensive to manufacture, but its performance is similarly limited, as described herein. It has only two parts (front and rear), and one pivot. Companies having a sufficiently large advertising budget can charge a high price and have a big profit margin on the suspension/bike, despite the marginal performance of the xe2x80x9chigh single pivotxe2x80x9d suspension.
3. Unified Rear Triangle.
Used by Trek, Gary Fisher, Klein, Schwinn, Ibis, and others.
This is a newer single pivot that was introduced once the buying public figured out the shortcomings of the Single High Pivot discussed in the preceding section. Although the unified rear triangle is better than the Single High Pivot in most regards, it is not significantly better.
The basic operating principle of these devices is illustrated in U.S. Pat. No. 5,474,318 to Castellano. This design has a number of positive attributes: it provides correct natural frequency of the suspension, thereby allegedly avoiding any pedal-force-produced bobbing; the entire bicycle drivetrain (including the cranks, and thus the pedals and the entire bottom bracket assembly) is contained with the unsprung structure of the rear suspension, thereby eliminating any chain-induced suspension bobbing and pedal kickback; using the rider""s legs as part of the unsprung structure of the rear suspension purportedly allows the rider to xe2x80x9cadjustxe2x80x9d the suspension on the fly by consciously stiffening or loosening his legs; positive shifting due to lack of suspension-induced chain whip; it can be somewhat non-pedal-torque reactive depending on pivot location; provides a relatively smooth ride while seated, with no kickback effect through the pedals; and is a very simple design.
Nevertheless, suspensions of this type have some important limitations. They can be very pedal-torque-reactive depending on the pivot location. Bicycles with this suspension design usually suffer from a severe pedal-force-induced bobbing effect. The suspension effectiveness becomes compromised when a rider is standing, to a very large degree in some designs depending upon pivot location. This problem is substantial, in view of a rider""s natural tendency to stand so that their legs can be used as shock absorbers and to improve their balance in extreme conditions. A unified rear triangle suspension becomes less effective while the rider is standing because the cranks and thus the pedals are attached to the rear xe2x80x9ctrianglexe2x80x9d (which is the unsuspended structure of the bike frame), which is the opposite of what is needed (riders typically stand during extreme conditions, when shock absorption is needed most). Depending on the pivot location, brake torque usually causes these designs to compress and pre-load or extend and lock up. This design also usually suffers from an extreme lack of rigidity during out-of-line loading (such as occurs during cornering) due to using a single pivot which has approximately the same moment arms with respect to the wheel""s contact patch (the area where the tire contacts the ground) as does the wheel""s axis. When cornering or under similar loading conditions, that near identity of moment arms provides very little, if any, resistance to sideways twisting of the wheel. Because of this, the pivot, frame and swingarm must be overbuilt to maintain sufficient strength.
In contrast, the preferred embodiment of the invention has the crank and pedals attached to the suspended frame member (the front section of the frame), so that the rider gets the benefits of being xe2x80x9csuspendedxe2x80x9d (shock absorption, etc.) regardless of whether the rider is sitting or standing. Moreover, the preferred embodiment of the invention includes a linkage with moment arms (with respect to the wheel""s contact patch) that provides substantial resistance to wheel twisting during cornering and the like, without having to overbuild the size of the components.
Perhaps as a result of the shortcomings of the unified rear triangle design, it has never (to the knowledge of the inventors) been raced by a factory team of any of the major companies in the bicycle industry.
4. Multilink, Low Main Pivot.
Used by GT, Turner, Intense, KHS (the foregoing are all four-bar linkage designs) Ventana, Mongoose, and Diamond Back (the last three utilize a swing or bell crank linkage).
The basic operating principle of these devices is illustrated in U.S. Pat. No. 5,441,292 to Busby and U.S. Pat. No. No. 5,678,837 to Leitner. The ride quality is improved by isolating bending moments from the front triangle by relocating the shock absorber to the rear link area of the suspension. The shock absorbers"" motion ratio is held close to linear due to the positioning of the shock absorber and links. The wheel travels in a near vertical path, instead of an arc, thus increasing shock absorbing efficiency and reducing energy wasting wheel fore and aft oscillations. Although some but not all four bar links are currently the most mature designs and are acknowledged by many people to be the best functioning of the current designs (because, among other things, a skilled designer has full control over shock motion ratio, brake torque reaction, and pedal torque reaction), there are still a number of disadvantages to the design. For example, currently most bikes using this design have been developed by trial and error with no clear understanding of all of the aspects of suspension function. Although some prior art linkage designs may approach the functional performance of the ICTT(trademark) suspension (that of the present invention) in one aspect of suspension functionality, no single prior art design effectively addresses all of the identifiable aspects of suspension function as does the ICTT. Among other things, prior art designs do not move the instant center to xe2x80x9ctrackxe2x80x9d and thereby cancel chain torque. Indeed, similar to that mentioned above in connection with the ""679 patent, the four-bar suspension system of the ""837 patent tends to prevent xe2x80x9cjackingxe2x80x9d by creating a binding action resulting from the interaction of the torques created to counteract the chain-induced torques, instead of canceling chain torque by causing the instant center to track the chain torque line, as does the preferred embodiment of the instant invention. Designs range from relatively good (having superior suspension performance characteristics) to xe2x80x9cRube Goldbergxe2x80x9d ridiculous. However, all of the current multilink designs suffer from at least one of the previously-identified faults: pedal torque reactivity, brake torque reactivity, bump induced pedal kickback reactivity, binding or stiffening of the suspension under pedal loads, improper shock motion ratio, and/or overly complex design. The relative flexibility of this design concept has resulted in some bizarre functioning, ill-conceived machines. Among other things, more parts, more material, results in higher manufacturing and maintenance costs and additional weight.
It is, therefore, an object of the invention to provide a suspension useful, for example, in connection with the rear wheel of a bicycle such as a mountain bike, which overcomes all of the shortcomings mentioned above.
Among other things, it is an object of the invention to provide a wheel suspension in which the instant center of that suspension substantially tracks the line of chain torque, thereby allowing the drivetrain and power through the drivetrain, be it from the pedals or the bumps, to be completely isolated from the suspension system and the forces it must respond to, and function from, including bumps, braking, etc. And at no time should the drivetrain""s ability to conduct energy to the rear wheel be negatively affected or have a negative effect on the independent operation of the suspension function; thus reducing or eliminating chain torque force loss or effect due to one suspension attached to the bicycle and canceling the undesirable loss of pedal stroke power or loss of suspension function at any time.
It is an additional object of the invention to provide a wheel suspension in which, for any compression position of the suspension, the instant center always falls between the maximum and minimum chain force lines. This provides the opportunity for a rider to select a gear (between the range of maximum and minimum) that very closely or exactly hits the IC, regardless of the compression position.
Another object of the invention is the provision of a suspension that isolates brake torque and its negative effects.
Yet another object of the invention is the provision of a suspension in which the shock motion ratio of the frame is linear or linearly progressive.
A further object of the invention is the provision of a wheel suspension in which xe2x80x9coff-the-shelfxe2x80x9d components may be readily used, such as gear sets, drive trains, brakes, etc.
Another object of the invention is the provision of a suspension in which a desirable amount of anti-squat is provided.
Yet a further object is the provision of a method of designing bicycle frames, which assists the designer in balancing various attributes of the frame and bicycle and suspension. Such method can include, among others, steps of:
identifying the average (or constant, if in a single chain line system is used rather then a cluster of gears and several chainrings as described in the preferred embodiment herein, which is currently the norm or industry standard gearing systems for high performance bicycles) chain torque line of a given set of gears or of a single gears while the bike is in a laden position. Bikes are not ridden in other then a laden position, so good suspension design takes into account the weight of a rider and the resulting normally laden suspension position;
selecting a location on that chain torque line that represents the desired IC for the frame. Factors affecting this selection include the amount of anti-squat (as discussed herein) one desires to build into the system. Also, and as described elsewhere herein, the desired motion ratio of the linkage affects the selection of the IC position, and typically the shorter the linkage and closer the IC to the suspension, the less effectively the suspension""s IC will track the Chain Torque Line, and less effective the Brake Torque Isolation will be. To lower the percentage of anti-squat, the IC needs to be further out (toward or beyond the front wheel); to increase the percentage of anti-squat), the IC needs to be closer to the rear wheel. Motion ratio is improved by selecting a rocker arm length close to that of the lower swingarm. To provide desirable Brake Torque Isolation performance, the rear of the link must permit brake loads to be imposed at near 90 degrees (nearly perpendicular) as described elsewhere herein;
using that selected location as the origin, projecting from that origin to select upper and lower axes for the frame members of a 4-bar (or other) suspension linkage. For 4-bar linkages utilizing the method of the invention, the lower rear pivot needs to be sufficiently close to a line between the rear axle and the center of the crank to avoid having that pivot hit by standard (off-the-shelf) derailleurs; the front lower pivot similarly needs to be sufficiently low to avoid being hit by any front derailleur and to ensure that the derailleur can be mounted at all, and sufficiently high to avoid excessive width behind the bottom bracket area (which width might, for example, cause mud to excessively collect and block the rotation of the tire in adverse conditions). Persons of ordinary skill in the art will understand that there are many other clearance issues in this area of frame and bicycle design, to make sure that the parts (especially those that move) do not undesirably rub, hit, or otherwise interfere with one another. The lower pivot locations must also be out of range of the rear derailleur to avoid xe2x80x9cchain slapxe2x80x9d (contact between the chain and the suspension structure, such as occurs in the many current art designs (Specialized, GT, AMP, etc.));
selecting the location for a shock absorption member. This location is preferably chosen so that standard (off-the-shelf) shock sizes can be used, and preferably to permit using a shock with sufficiently long stroke to keep the motion ratio low (as discussed herein) and to avoid excessive loads. Preferably, the shock is located and configured within the linkage so that the angles of the shock in relation to the linkage provide for a linearly progressive or straight rate motion ratio;
selecting the lengths of the various linkage arms (some of the preceding section also relates to selecting the lengths of the linkage arms). In the preferred embodiment, particularly the length of the upper link (between the upper pivot points) is based on the desired travel (total movement up and down of the linkage) for the linkage as well as the desired motion ratio of the suspension (which may, for example, allow for a broad selection of shock mediums). In addition, the design (including the linkage arm lengths) needs to take into account structural forces such as where various loads will intersect the front structure (such as elements 1-4 in FIG. 1). For example, loads applied in the middle of the seat tube 1 may lead to premature failure of that tube 1 under extreme loading situations. In the preferred embodiment of the instant invention, linkage arms (and their associated force loads) attach close to tube intersections of a generally conventional xe2x80x9cfront trianglexe2x80x9d (such as represented by elements 1-4 in FIG. 1), to utilize the strength of those intersections. The amount of linkage travel can be adjusted by manipulating the ratio between the length of the front (or nose) of the rocker (the length of arms 6, 7 from pivot F forward) and the rear of the rocker (the length of arms 6, 7 from pivot F back to pivot E). Also, in 4-bar linkages such as the preferred embodiment, the length and location of this upper swingarm must be carefully coordinated with the length of the other suspension structural members to achieve the desired amount of BTI (Brake Torque Isolation geometry). As discussed herein, the angle between the suspension structural members attached to the upper rear pivot can directly affect and determine the BTI of the suspension. If the upper linkage arm is too short, not only will the suspension IC not closely track the chain torque line, the suspension will not provide desirable BTI geometry to reduce or eliminate problems from brake torque loads. Such brake torque load problems are very common in current four-bar linkage designs (including the TRUTH shown in FIGS. 13a-c, GT STS/LTS designs, Specialized FSR designs and others);
generally, from the beginning or from this point on, CAD (computer-aided design) modeling of a myriad of configurations can help determine the best possible configuration to achieve a desired balance between the elements of the design. Among other things, CAD modeling of loads and torques can help determine a desirable configuration to establish and maximize ICTT of the chain torque, the closest possible BTI geometry to reduce or eliminate the effects of Brake Torque on a suspension linkage, maintain a near-vertical wheel travel path, keep linkage motion ratio and shock motion ratio in the desired range, and select the packaging, complexity of manufacture and ability to utilize industry standard parts;
design the parts. The rockers (the upper swingarm), being long and low (the rockers"" position is preferably low relative to most current art, which allows the bike of the invention to have a low standover height with a relatively large amount of travel), preferably maintain good stiffness torsionally from wheel twisting loads on the linkage. The preferred embodiment and method further includes a one-piece machined swingarm yoke and a shockstay clevis machined from a solid piece of material, to help maintain near-perfect alignment and excellent strength. Also, the xe2x80x9cRocker Blockxe2x80x9d (see FIG. 2J) helps maintain a desired amount of rigidity in the upper rocker arms without interfering with or contacting the tire and seat post (which move between the rocker arms while the linkage is in motion).
In addition to providing a solution to each of the various problems discussed above (many or all of which could be utilized in a suspension design without the other elements of the invention), the various solutions can be practiced in a variety of combinations with each other, and are preferably all included in the preferred embodiment and methods.
Our preferred design is also very light and simple, which minimizes the disadvantages of weight (indeed the preferred embodiment of the 7xe2x80x3 travel Dare weighs between 15%-50% less then it""s nearest competitors. Literally, it is the lightest 7xe2x80x3 travel FS bike in the world today. In fact the Dare weight is comparable to the shorter 4xe2x80x3 travel cross country offerings of Specialized, Turner, GT and Intense), but even more importantly, our design greatly reduces or eliminates the xe2x80x9cpower suckingxe2x80x9d of chain torque and other loads that occur with prior art designs, as discussed above.
We sometimes refer to the invention as Instant Center Tracking Technology (or xe2x80x9cICTTxe2x80x9d). We created and developed ICTT to eliminate the foregoing suspension design problems. In its preferred embodiment, ICTT is characterized by a four-bar linkage with specifically positioned pivot points and one or more shock absorption elements, resulting in improved performance through, among other things, desirable alignment of various force and torque lines over the range of expected rider loading, pedaling, and shock impacts.